Methods for producing 2-cyanoimino-1,3-thiazolidine from the reaction between dimethyl N-cyanoiminodithiocarbonate ester and 2-aminoethanethiol, are those described in Arch. Pharm. (Weiheim, Ger.), 305 (10), P731 (1972), Japanese Unexamined Patent Publication (Kokai) No. 48-91064, Gazz. Chim. Ital., 110 (5-6), P345, and WO92-17462 (1992). This reaction is considered to follow the following formulas: 